Petroleum based feedstocks include impure petroleum coke and other hydrocarbonaceous materials, such as solid carbonaceous waste, residual oils, and byproducts from heavy crude oil. These feedstocks are commonly used for gasification reactions that produce mixtures of hydrogen and carbon monoxide gases, commonly referred to as "synthesis gas" or simply "syngas." Syngas is used as a feedstock for making a host of useful organic compounds and can also be used as a clean fuel to generate power.
The gasification reaction typically involves delivering feedstock, free-oxygen-containing gas and any other materials to a gasification reactor which is also referred to as a "partial oxidation gasifier reactor" or simply a "reactor" or "gasifier." Because of the high temperatures utilized, the gasifier is lined with a refractory material designed to withstand the reaction temperature.
The feedstock and oxygen are intimately mixed and reacted in the gasifier to form syngas. While the reaction will occur over a wide range of temperatures, the reaction temperature which is utilized must be high enough to melt any metals which may be in the feedstock. If the temperature is not high enough, the outlet of the reactor may become blocked with unmelted metals. On the other hand, the temperature must be low enough so that the refractory materials lining the reactor are not damaged.
One way of controlling the temperature of the reaction is by controlling the amount of oxygen which is mixed with and subsequently reacts with the feedstock. In this manner, if it is desired to increase the temperature of the reaction, then the amount of oxygen is increased. On the other hand, if it is desired to decrease and temperature of the reaction, then the amount of oxygen is decreased.
Conventionally, the oxygen to be utilized in the reaction travels via a pipe from an oxygen source to a compressor and then through a second pipe from the compressor to the gasifier. There is often a reservoir between the compressor and the gasifier. At the gasifier, the oxygen is introduced through a port at the upper end of the reactor to mix with the feedstock. Control of the amount of oxygen which enters the port is accomplished by using a valve at the port. When the valve is open, oxygen flows into reactor. When it is necessary to slow the reaction and cool it, for instance, when the flow of feedstock has slowed, then the flow through the valve is reduced, i.e., the valve is moved to a reduced flow position.
Unfortunately, the above-described control system does not control the oxygen very precisely. This is due to the fact that even when the valve at the port is in the reduced flow position, oxygen is still being sent through the second pipe by the compressor. The produced oxygen travels from the compressor to the reduced flow valve and the oxygen pressure increases. Therefore, good control is difficult to achieve.
One solution is to have a large reservoir on the compressor outlet. However, this is a great safety hazard, since there are high temperatures and carbonaceous materials nearby. It would be desirable if a method and system for controlling the flow of oxygen in a gasification process could be discovered which directly reduces the amount of oxygen in the pipeline.